The invention relates to a process for removing sulfate ions from organic sulfates and sulfonates and, if required, low molecular weight organic sulfonates/sulfates particularly from aromatic sulfonates and sulfate or aliphatic sulfonate and sulfate compositions. The invention is particularly directed to the removal of sulfate ions from alkyl naphthalenes and alkyl benzene sulfonates, naphthalene sulfonates and the oligomeric materials formed by reaction of the aromatic sulfonates with aldehydes, preferably formaldehyde. Typical materials which can be treated by the process of the present invention are disclosed in U.S. Pat. No. 4,465,492 which is incorporated herein by reference. The organic sulfates or sulfonates or mixtures thereof contain sulfate ions in the form of an acid or salt which results from use of excess sulfonating material used in their preparation. The term organic sulfonates/sulfates as used herein refers to the organic sulfonated or sulfated material or mixtures thereof.
The process for sulfonating naphthalene is described by E. A. Knaggs, "Sulfonation and Sulfation", Encyclopedia of Chemical Technology, Vol. 2, p.145 (John Wiley & Sons, Incorporated, New York, New York, 3rd Ed., 1983), the disclosure which is incorporated herein by reference.
The materials which can be treated by the present invention include the condensation polymers of a condensible carbonyl compound and an aromatic sulfonate. Preferred examples of such condensates are formaldehyde condensates of naphthalene sulfonic acid and formaldehyde condensates of lower alkyl substituted naphthalene sulfonic acid. Other examples are aromatic-based carbonyl condensates including condensation products of acetone with naphthalene sulfonic acid or benzene sulfonic acid.
Sulfonated aromatic compounds and particularly sulfonated (alkyl)naphthalenes can be employed in the manufacture of the condensates. The term (alkyl)naphthalenes or (alkyl)benzene refers to naphthalenes and benzenes or their alkyl-containing homologs. However, as an alternative to pre-sulfonation, the naphthalene can be sulfonated during condensation with the aldehyde. Condensation and sulfonation produces a product which is considered a naphthalene aldehyde sulfonic acid or naphthalene sulfonic acid-aldehyde condensate. The processes for preparing the condensates are described in U.S. Pat. No. 2,141,569 (Tucker et al.), issued Dec. 27, 1938, U.S. Pat. No. 3,193,575 (Neville et al.), issued Jul. 6, 1965, and U.S. Pat. No. 3,277,162, Johnson, issued Oct. 4, 1966, the contents of which are incorporated herein by reference. Condensation products generally have a number average molecular weight of from about 1,500 to about 6,000 and a weight average molecular weight of from about 3,000 to about 16,000 and will contain up to about 8 to 30% by weight of non-condensed materials such as mono- and di-sulfonated aromatic materials. Composition with higher and lower number average or weight average molecular weight can be treated to remove sulfate ions from the composition.
The (alkyl)naphthalene sulfonic acid formaldehyde condensation products comprise a mixture of condensation products of (alkyl)naphthalene sulfonic acid and formaldehyde. The condensation products differing for example in the degree of polymerization. The mixture can be separated by size-exclusion chromatography to selectively separate the molecular species according to size. This is one method for obtaining a measure of the degree of polymerization.
The aromatic aldehyde condensates are generally water-soluble or water-dispersible and contain substantial amounts of sulfate (up to about 15 to 20% by weight of the solids) depending upon the ratio of the sulfonating agent to the aromatic compound. Depending upon the commercial use for the material, the level of sulfate in the composition must be reduced. If a high-salt form of the composition is required, the unreacted sulfuric acid is merely neutralized and the condensate containing the neutralized sulfuric acid can be sold for certain uses.
If a low-salt material (less than about 3.0-6.0% by weight of the solids) is required, the sulfate ions must somehow be separated from the aromatic sulfonate aldehyde condensation product. This can be accomplished by neutralizing the unreacted sulfuric acid with an alkaline material such as calcium hydroxide and separating the calcium sulfate formed from the aromatic sulfonate-aldehyde condensation product. However, the water solutions or dispersions generally have a high viscosity and the filtration can be difficult. The mixture of calcium sulfate with the aromatic sulfonate-aldehyde condensation product must also be disposed of. This is an expensive problem because the amount of raw materials that is converted to filter cake is substantial and the filter cake must be disposed of in a hazardous waste material disposal facility. In addition to the aforementioned expenses, the material also carries with it a portion of the aromatic sulfonate-aldehyde condensation product.
In view of the disposal problems and the cost of the raw materials to neutralize the excess sulfate, processes for preparing the aromatic sulfonate aldehyde condensation products are generally optimized to provide the required sulfonation utilizing the minimum amount of excess sulfuric acid. The diagram of a known process requiring neutralization and separation of calcium sulfate for preparing the aryl sulfonate aldehyde condensation products is set forth in FIG. 1.
The presence of the sulfate salts and the unpolymerized and uncondensed aryl mono- and di- sulfonates has a deleterious effect on the use of the condensation products as a cement additive. It would be useful to be able to easily reduce the amount of sulfate and the amount of unpolymerized or uncondensed aryl sulfonates in the composition.